The standard model of star formation applied to massive stars: accretion discs and envelopes in molecular lines

We address the question of whether the formation of high-mass stars is similar to or differs from that of solar-mass stars through new molecular line observations and modeling of the accretion flow around the massive protostar IRAS20126+4104. We combine new observations of NH3(1,1) and (2,2) made at the Very Large Array, new observations of CHCN(13-12) made at the Submillimeter Array, previous VLA observations of NH(3,3), NH(4,4), and previous Plateau de Bure observations of C34S(2-1), C34S(5-4), and CHCN(12-11) to obtain a data set of molecular lines covering 15 to 419 K in excitation energy. We compare these observations against simulated molecular line spectra predicted from a model for high-mass star formation based on a scaled-up version of the standard disk-envelope paradigm developed for accretion flows around low-mass stars. We find that in accord with the standard paradigm, the observations require both a warm, dense, rapidly-rotating disk and a cold, diffuse infalling envelope. This study suggests that accretion processes around 10 M stars are similar to those of solar mass stars.